Agriculture Reference
In-Depth Information
Fig. 4.3
Contour farming in a sloped fi eld (From USDA NRCS
2013
)
guidance is impossible. In many cases this means that one or a few passes in a
circuitous pattern are necessary around a fi eld and apart from that the main area
inside these passes is handled in fi xed line guidance. The number of headland turns
can be minimized by choosing the longest fi eld side respectively for the direction
of the fi xed lines.
In sloped regions with continental climate, often
contour farming
(Fig.
4.3
) is
essential since it substantially can reduce runoff of water, thus also can diminish soil
erosion and improve water infi ltration into the land. This implies guiding the
machinery as far as possible along lines of similar elevation, hence straight paths
hardly are possible and curved lines in most of the area must be dealt with. As long
as the curvature is constant, this does not prevent the use of fi xed line guidance. Yet
when variations in curvature show up, prior pass guidance as outlined above is needed.
All in all, guidance with contour farming is more complicated and often less precise.
4.2
Techniques of GNSS Based Guidance
Two main techniques are available, either the lightbar- or the automatic guidance
system. The former often is also denoted as the manual guidance system.
Both techniques rely on GNSS signals for the indication of the cross-track errors.
These are the deviations of the horizontal distance to the reference line, which can
be the prior pass- or the fi xed line as well as any offset line to it.
With the
lightbar guidance system
, the cross-track errors are indicated in a
display by means of light emitting diodes (LEDs), which are arranged in a horizon-
tal row (Fig.
4.4
). The errors that occur from pass to pass depend on the guidance
principle as well as on the driver because the steering is still manual. However, in
